Toggle "Resize display to fill window size" in game (Need help!)

[fishrod]

"Resize display to fill window size"
Is a option in mmf2 when clicking the application icon.
I have this option enabled and want to disable it ingame I don't it's possible without extension.
I tried ultimate fullscreen this doesn't work for me.
If someone knows how to do this or has a good extension for me please let me know.
Because this problem is bugging me for a long time if someone could help I really appreciate it and could continue without problems for now.
Thanks!

[fishrod]

I downloaded some templates.
Tested things out but how can you stretch a frame that is 1920x1080 in a window that is 1600x900 so you can see the whole frame?

[fishrod]

I tested it the only difference is the frame isnt centered but you view the corner now.